Relativistic Heavy Ion Collider

The Relativistic Heavy Ion Collider (RHIC) is a particle collider at Brookhaven National Laboratory that collides heavy ions and polarized protons to study nuclear matter and spin.

Heavy-ion collision: A collision between atomic nuclei accelerated to high energies, producing conditions that can resemble those of the early universe. RHIC creates these collisions to probe matter at extreme temperature and density.
Quantum chromodynamics: The quantum field theory describing strong interactions among quarks and gluons. It supplies the theory RHIC measurements test under extreme conditions.
Brookhaven National Laboratory: A U.S. Department of Energy research laboratory on Long Island, New York. RHIC was built and operates at Brookhaven.
Spin physics: The study of intrinsic angular momentum and its role in physical systems and interactions. RHIC’s polarized-proton collisions investigate how quarks and gluons contribute to proton spin.
Perfect fluid: An idealized fluid with zero viscosity and no dissipative stresses. RHIC measurements showed that the quark–gluon plasma behaves like a nearly perfect fluid.
Relativistic kinematics: The description of motion and collisions when particle speeds approach the speed of light. RHIC’s beam energies require relativistic accounts of particle motion and collision products.
Nucleon: A proton or neutron, the principal constituents of atomic nuclei. RHIC collides nuclei built from nucleons and protons whose internal structure it probes.
AGS: A Brookhaven particle accelerator that has served as an injector and research machine. The Alternating Gradient Synchrotron supplies ions to RHIC’s accelerator chain.
Beam energy scan: A program that varies collision energy to map changes in the properties of matter produced in collisions. RHIC’s scan searches for changes in the nuclear phase diagram, including a possible critical point.
Quark–gluon plasma viscosity: The resistance to flow of the quark–gluon plasma, commonly characterized by shear viscosity relative to entropy density. RHIC flow data constrain this unusually small viscosity and the plasma’s dynamics.

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